The Diablo Range is one of many north/south mountain ranges on the western side of California. Well-known peaks in the range include 37.5124-121.8811 Mission Peak (2,520 ft (770 m)), 37.881698-121.9141552 Mount Diablo (3,849 ft (1,173 m)), and 37.341667-121.6430563 Mount Hamilton (4,265 ft (1,300 m)). Toward the southern end of the mountain range is 36.3696-120.6454 San Benito Mountain , the Diablo Range's highest point. Mount Diablo can be seen from miles away due to its prominence.

The mountains in the range consist of ridges, which are high enough to make a difficult hike but not high enough to be considered a major mountain range by U.S. standards. The western end of the Diablo Range is a few miles inland from the San Francisco Bay, east of the cities that exist along the shoreline. It continues north to the Sacramento Delta, which effectively cuts off the northern end of the mountain range by connecting the San Pablo Bay with the Central Valley. South of the San Francisco Bay, the Diablo Range becomes connected by land to the Coastal Ranges along the west coast of California. There is, however, a valley south of San Jose (the location of Coyote Creek) which separates the Diablo Range from the ranges closer to the Pacific Ocean. The eastern edge of the Range slopes into the low-lying, agricultural Central Valley, near cities such Tracy and Patterson. The network of mountain ranges in this part of the state is complex, and where a mountain range ends and another begins is not always straightforward. The Diablo Range can be considered a "coastal range" but is not on the coast, but since at its southern end it is intertwined with the Coastal Range, identifying the mountain range of some destinations, such as the Pinnacles, is marginal.

The eastern side of the East Bay region extends into the mountains, and the 37.701208-121.9228365 Tri-Valley is between two parts of the range, with the friendlier peaks to the west and wilderness to the southeast. To the north of the Tri-Valley is Mount Diablo. To the east of 37.685556-121.7641676 Livermore, one of the main cities in the valley and one of the largest cities within the Diablo Range, is Altamont Pass with its wind turbines and dry hills. Particularly the north, due to its proximity to the Bay Area, is more densely populated, while the mountain range's population is lower south of the Tri-Valley.

The mountains and ridges vary in height, but as a general rule are separated by canyons, with creeks usually at the bottom of the canyons. The creeks may flow year-round if their source is a reservoir. Alternatively, they may flow seasonally, when rain falls, or may almost never turn into streams. The Alameda Creek—which flows through Niles Canyon—is moderately wide for a significant portion of its distance, but most are narrow and carry little volume due to the region's semi-arid to moderately wet status.

While Mount Diablo stands out as a mountain on its own (it is one mountain with two peaks), most of the mountains in the Range do not have such prominence and are buried either in ridges or behind other mountains. Diablo, like many of the ridges and mountains in the range, is not beautiful; those who seek the beauty of this region will need to find the hills and valleys, not the highest points. The Diablo Range can be dramatic, and many parts of the region resemble the Old West, with the distinction of being nearer urban areas than anywhere typically thought as "western" or "cowboy country." Looking one way, you can see how rural California looked a hundred years ago, and looking another way, you can get breathtaking views of one of the most modern and developed urban areas in the world.

The hills in the Diablo Range are covered in medium-length, yellowish grass during most of the year; grass usually turns green following precipitation in winter and spring. Oak trees are scattered all over some hills, but are completely lacking on others. One side of a ridge will, in many cases, contain far more trees than the other side. California poppies are quite common in some parts of the range, but they do not last long and you are lucky if you arrive during the poppy season. The most accessible parts of the Diablo Range feature either grasslands or oak, although flora becomes dense in the immediate vicinity of a stream, and near some there are larger plants such as eucalyptus and sycamore. The oak trees are, in most cases, small, though this depends on precipitation. Palm trees are rare, and they struggle in the wild. Western parts of the range tend to feature more flora than the east, which is semi-arid due to the rain shadow effect.

Deer live in hospitable locations, but are not common. Animal life is limited; snakes, rodents, and certain kinds of birds (like turkey vultures) are the most common creatures. There are some eagles and the rare California condors (see Pinnacles National Park article) as well, but birds of prey, herons, or particularly panthers are rare sights.

The cities of the East Bay are all either inside or near the Diablo Range. Similarly, 37.304167-121.8727787 San Jose and some of the other cities on the east side of the South Bay are close to the Diablo Range. An example of a settlement that is truly inside the range is 37.941111-121.9358338 Clayton. East of the mountains and on the western side of the Central Valley is 37.738056-121.4338899 Tracy. On the western side of 37.6725-121.882510 Pleasanton and the eastern side of 37.668889-122.08083311 Hayward/37.71-122.0612 Castro Valley are some housing developments going into the hills. However, as the focus here is on visiting the Diablo Range, please refer to each city's article to find out more about it.

In summer 2020 the largest fires in the state's modern history impacted mountain regions, particularly in those on the western side of the state, and the Diablo Range was one of the most severely impacted. Hundreds of thousands of acres were burned and it will likely be some time before the region returns to the beautiful scenery it had possessed. The fringes, though, were not so severely impacted, and as many of the parks noted here are in the foothills of the mountain range nearer to cities and towns, many of them have not been affected as much as the interior.

See also: Outer East Bay#Get in

You should enter the range by car so that you have a vehicle to use once you're inside the mountain range itself. Public transportation is almost nonexistent within the Diablo Range, with the exception of the ACE Train and BART in the East Bay. These don't cover nearly enough of the region to be used to explore the mountains.

There are roads that lead in from the outside of the range to the Tri-Valley area, which is a good starting point if you then want to get to parks and mountains.

In the north, there are some freeways that go through the Tri-Valley area; for example, I-580, which goes across the range (meaning that you can use it to enter the range from either east or west), and I-680, which goes from Silicon Valley to the Tri-Valley, and then continues north from there. You can come across the Sacramento Delta and enter the mountainous parts of the East Bay by taking I-680 south. Generally, if you're looking to enter the northern part of the range via interstate, you take I-580 from the west or east or I-680 from the southwest or north.

A more scenic way to enter the mountain range is the section of California Route 84 between Niles (a neighborhood of Fremont) and Sunol. Route 84 goes through Niles Canyon, the location of Alameda Creek and a railroad. Since this part of CA-84 follows the bottom of the canyon and links important city areas, heavy traffic is common despite the challenges of the drive. However, the road is two-way from start to finish, and is quite straight and quick in some places. The road should definitely be avoided during flooding or a serious rainstorm, since there are high banks with steep hills alongside the road, making landslides dangerously likely. The canyon, however, is truly beautiful, with the creek at the bottom, the mountains on each side, and the railroad. (There are a couple railroad bridges along the canyon, though these in beauty do not match the surroundings.) Additionally, to the east of Niles Canyon, a section of CA-84, goes east from I-680 through hills near Pleasanton and Livermore. This road, though, is generally not such a pleasant drive, as it is an expressway most of the way.

If you're coming down from the north (for example, from Brentwood), a worthwhile option is Vasco Road. Like CA-84, it's popular with commuters, unfortunately, and isn't quite a country lane anymore, but it does go through the northern part of the Diablo Range in a region that otherwise is not too developed. The northern and southern ends of the road go through cities, but the long middle section is still very much in the country. North of Livermore is a turn-off road that leads to 37.82025-121.733813 , a popular fishing destination.

BART goes to Pleasanton, a city within the northern part of the Diablo Range, from Oakland and San Francisco.

If, for some reason, you cannot get into or around the Diablo Range by car, there are plenty of local taxis, although these are fairly expensive.

A good base for exploring the Diablo Range is the Tri-Valley, as it is a wide, populated valley inside the range that offers many roads leading into the mountains themselves; these include Mines Road from Livermore to the south and many other roads leading in various directions to parks and other sightseeing destinations. Of the major California routes US-101 goes to Morgan Hill and San Jose, which are west of the range, and I-5 goes from south to north, east of the range. From any of the roads in suburban areas, you'll have to take various roads to get into the mountains.

You can't drive north/south through the whole range because the terrain is simply too rugged, and generally there are not enough people living in the mountains to justify highways of any sort. You can do a few roads, like Mines Road (mentioned in #Do), and other roads in the northern part of the mountain range, for transport to particular points in the range, but mostly you should take roads like U.S. 101 or I-5 if you want to get from one part of the range to the other. For example, if you were going from Mount Hamilton to Henry Coe Park, you would use one of the major roads that goes west, parallel to the mountains.

Roads in the mountains are variable: some of the roads out in the wilderness, like the Mount Hamilton Road, are best taken slowly, while suburban roads are, on the whole, well-maintained and designed. There are sometimes one-lane roads, like Laughlin Road to Brushy Peak Regional Park. Apply the same cautions you would normally apply to one-lane roads. On the other hand, some country roads are excellently kept, and form some of the safest and most pleasant drives you can experience: good examples include Wetmore Road and Arroyo Road in the Sycamore Grove/Del Valle area on the southeast fringes and outsides of Livermore.

The Diablo Range is a fairly large area, though not too large by American standards. It takes a few hours to drive to some of the parks, especially if your base for exploration is far in the north or the south of the Diablo Range. If you are going from somewhere near the Sacramento Delta, north of Mount Diablo, all the way south to the Pinnacles and back, expect a long drive each way. On the other hand, navigating around the East Bay, especially if you start in a central location, should not require great distances of travel. Driving in the mountains tends to be slow, while freeways, when traffic is good, should keep you moving at 60 miles per hour; when you're planning to go somewhere, if you don't have GPS directions readily available, take the conditions of the drive into account—you'll want to take some rural roads very slowly, while others will be good for a faster pace, especially if the terrain is good.

The Tri-Valley has a good network of surface streets, avenues, and boulevards that can be used for getting around the towns.

As this is California, and quite an expensive region of the state, gas prices are high.

See also: United States without a car

Generally, you can throw public transport right out, since getting to country parks requires driving. For sightseeing, however, which is covered in the next section, there are some alternative options available.

As there are large distances at stake in the Diablo Range, and getting from place to place often requires distances, walking is also out of the question. Of course, there are plenty of hiking opportunities throughout the Diablo Range, but those are recreation rather than travel. The Tri-Valley looks small on the map, but it is actually large on its own, and the extent of the mountains around it is of course much more. Do not take for granted distances, which is why cars are so important here.

An official guide to navigating the Bay Area, 511.org, exists. Particularly the Contra Costa division applies to the Diablo Range area.

Mount Diablo is rather an interesting mountain for viewing, since its appearance varies greatly depending on the side from which you see it, and unlike other mountains in the Diablo Range, it is easily recognizable. The best view of Mount Diablo is from the south, around Pleasanton and eastern Dublin. Mount Diablo's neighbor, North Peak, is similar in height and grandeur.

To view Mount Diablo from a distance, just find an open area near Pleasanton or eastern Dublin and look for the largest mountain to the north to see the peak. You can also view surroundings from the top of the mountain by driving the road that leads almost all the way to the top (it's not a short and easy drive, though). See Mount Diablo State Park for further information.

Mount Hamilton isn't so easy to spot from a distance; however, if you're in the San Jose area, look for a mountain with small, white spots on top — those white spots are Lick Observatory, which is near the peak of Mount Hamilton. However, the observatory, while it contains some huge, white telescopes, is quite a long way from San Jose and therefore is not easy to spot at first glance. It's better to view San Jose from the top of Mount Hamilton than to view the mountain from below, as the view is absolutely stunning from the surroundings of the visitor center. CA-130 (Mount Hamilton Road) ascends the mountain from the west, and San Antonio Valley Road approaches it from the east, with the two roads meeting near the observatory.

See also: Hiking in the East Bay

The Diablo Range is a good place for hiking. The East Bay Regional Parks District (EBRPD) has put a lot of work into creating many regional parks that have good trail networks. Meanwhile, there are also non-EBRPD parks with hikes worth doing: examples include Joseph Grant Park, Los Vaqueros Watershed, and Mount Diablo State Park. There are a few city parks and trails in the Diablo Range and vicinity.

Hikes vary greatly in difficulty, depending on the part of the range and, therefore, the sizes of the nearby ridges. Some of the lowest hills are only a very short climb, while the highest involve climbs of well over 1,000 feet (300 m) from a starting point that is, in turn, well above sea level. The rugged terrain of parks farther out into the countryside tends to be harder going, while the parks adjacent to cities have easier hikes; but this is not always true. EBRPD park maps display contour maps, which you can use to figure out which trail takes the flattest route.

On the whole, hiking is a joy in this region. The climate is friendly outside peak summer months and the coldest winter nights, and there are numerous hiking options.

This part of California has a large and important cycling culture; cyclists are a common sight on rural roads and in parks. If you want to cycle for recreation, however, check the route first; there are some relatively easy roads, but Mount Hamilton Road, for example, lacks a decent shoulder and is a challenging climb. In some towns, there exist paved trails for cyclists, but when cycling in parks in rural areas, make sure the trail surface is appropriate for cycling, as some have a lot of gravel or rocky path surface. Wider trails will generally be more appropriate than the narrow trails that steeply climb hills.

Sometimes, there are recreational events in which roads are closed or at least limited to traffic for cycling events.

If you are not a hiker, there are some interesting options available for driving through the area—for fun, of course. Driving for enjoyment is not possible in much of the Bay Area, due to traffic, but there are some country roads that are different.

• One of the best options is the road to the top of Mount Hamilton, also known as Lick Observatory, which begins in Alum Rock (San Jose). It's a challenging drive to the top, but actually that isn't the best part; the best part is the San Antonio Valley Road that continues into the wilderness east of Mt. Hamilton. Farther down the road there's a junction where you can either go east to Patterson or north to Livermore. At the intersection, quite surprisingly considering the remote location, there's a restaurant. The road north from this junction, toward Livermore, is called Mines Road. The road up Mount Hamilton is in the California highway system as California State Route 130.
• On a weekend, Patterson Pass Road, which goes from Livermore to Tracy and vice versa, is an enjoyable drive. It's more-or-less a one-lane road some of the time, and it goes into the hills, so take your time.
• Morgan Territory Road, up to the Morgan Territory Preserve staging area, is a worthwhile drive if you want to hike at that park. It goes up, into the hills; take Livermore Avenue north out of Livermore to get to the turning for Morgan Territory Road.

There are plenty of hotels in nearby cities (such as those in the East Bay and the Tri-Valley), so lodging is not a problem. As this is California, and an expensive part of the state, generally, expect hotels to be mid-range to expensive. Commonly, these are the large chains found in abundance in the U.S., such as Best Western or Super 8. You can find hotels along I-580 in the Tri-Valley; from these hotels, you can go north toward Mount Diablo, west toward the Pleasanton Ridge and that ridge's neighbors, and south toward Del Valle.

There are campsites, including in Del Valle Regional Park. These vary from just some open ground with picnic tables and a (disgusting) restroom facility to Del Valle's more full-blown campsite with parking spaces for camping vehicles and some facilities.

The advice in #Eat is worth carrying over here; the ground isn't wonderful, so you should bring towels or other objects to cover the ground. Some parks have designated camping spots out in the countryside (Del Valle and Henry Coe are two), and it is wise to keep to those. If you wander off a trail, you put yourself at risk if you find yourself in danger, particularly in parks with a lot of open space.

There are sometimes public toilets at various, usually picnic or campsite-related, locations, but these can be disgusting. Do not be surprised if weeds are growing next to the doorframe, soap disposal doesn't work properly, and the inside is dark. Unfortunately, this is the price you pay for not doing business in the place you're staying before you start hiking. If you are having a picnic, eat the food before you use the restroom, if possible. Some of these restrooms are not permanent structures and are not only for the visitors, and may be placed for shepherds and ranchers as well.

Dangerous animals that live in the area are mountain lions and rattlesnakes.

Rattlesnakes are known for being a problem in this region. The best way to avoid rattlesnakes by staying away from the edges of trails, if possible, so you will see the rattlesnake before it is dangerously close to you. (The worst time for rattlesnakes is the summer.) Although not all snakes are dangerous, and there are "good" snakes in the Diablo Range, if you're not a biology expert, it's best to be careful about all snakes in case you come in contact with a rattlesnake. If a rattlesnake is on the trail, and it is near you, step away from it — if the snake is front of you, go backwards along the trail, if possible, so you are safely away from the snake. Do not assume that, if a snake is a few feet (a meter) away, you are safe. If you keep distance from the snake, chances are that the snake will cross the trail and go into the grass; once he's well into the grass and several feet from you, you can resume along the trail.

The other animal-related safety issue is the mountain lion, which is the Diablo Range's equivalent to the black bear, in terms of danger. To avoid close contact with mountain lions, stay in open areas when possible; it's good to look around every so often, especially if you hear a suspicious ruffling of bushes or grass. If you do find yourself near a mountain lion, the advice usually given is that you should make yourself seem larger and more powerful than the mountain lion by reaching out with your arms and legs and by holding up large objects. Also, as is often the case with wild animal encounters, the mountain lion is probably as scared of you as you are of them and stay as confident as possible, and this fact is worth remembering.

Particularly in the lower regions of the park, extreme heat can be a problem, as temperatures can pass 110 °F (43 °C) in June, July, August, and September. In the park's highest elevations and Ohlone Regional Wilderness in particular, there can be snow, but temperatures never get bitterly cold in Del Valle or Ohlone (no negative degrees Fahrenheit) and the quantity of snow is rarely enough to be dangerous, even on the rare occasion when it does snow.

If it's a really hot day, do your activities fairly early in the morning and make sure you're done with them by 10-11 AM at the latest, depending on the expected temperatures. On a normal summer day, temperatures will still get hot at the peak, during the afternoon, but are unlikely to pass 100 °F (38 °C), so you should plan your activities depending on how used to the heat you are.

Respect is a very important issue in many wild areas, but the Diablo Range's parks are especially conscious when it comes to respecting wildlife. Litter is not common in the mountains and frowned upon. A strict attitude is taken, particularly in parks with reservoirs. While few parks ban dogs outright (Los Vaqueros Reservoir being an exception), rules pertaining to dogs are often complicated and strict. Cycling is very popular, however, and cyclists go off the path and create their own trails sometimes. However, the East Bay, especially inland, is a region with high standards and expectations, so you should not push the rules, whether it comes to cycling, dogs, or any other issue.

California has a strong environmentalist presence, but many other people in the region unfortunately care little about the beautiful scenery that surrounds them. It's a mixed bag, however, and development, especially in the hills, can be a controversial issue around elections and not one in which it is wise to be involved as a visitor. Even attempted permission for a small housing development receives wide-scale opposition, so work is being done to "save the hills," but again, this is an issue not to be pressed, as varying people have vastly different views that are often strong.